Certain hydrofluoroolefins (HFOs), such as tetrafluoropropenes (including 2,3,3,3-tetrafluoropropene (HFO-1234yf)), are now known to be effective refrigerants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike most chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), most HFOs pose no threat to the ozone layer. HFO-1234yf has also been shown to be a low global warming compound with low toxicity and, hence, can meet increasingly stringent requirements for refrigerants in mobile air conditioning. Accordingly, compositions containing HFO-1234yf is a leader among the materials being developed for use in many of the aforementioned applications.
A manufacturing process for HFO-1234yf, as e.g. disclosed in U.S. Pat. No. 8,058,486, uses 1,1,2,3-tetrachloropropene (HCO-1230xa) as starting raw material. The process consists of the following three steps: (1) HCO-1230xa+HF→2-chloro-3,3,3-trifluoropropene (HCFO-1233xf)+HCl in a vapor phase reactor charged with a solid fluorination catalyst, (2) HCFO-1233xf+HF→2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in a liquid phase reactor charged with a liquid hydrofluorination catalyst, and (3) HCFC-244bb→HFO-1234yf in a vapor phase reactor.
As also disclosed in U.S. Pat. No. 8,058,486, subsequent to Step (1) above, the effluent stream exiting the vapor phase reactor is fed to a first recycle column. The lighter components, including HCl, HCFO-1233xf, HCFC-244bb, HFC-245cb, and small amounts of HF, are isolated as a top light stream, and are fed to next unit operation as a crude first intermediate stream. The majority of the un-reacted HF and heavy intermediates are isolated as a bottom heavy stream, and are fed back to the vapor phase reactor of Step (1). Nevertheless, high boilers such as 1230xa dimers, e.g. C6H3F6Cl, C6H3F7Cl2, C6F6Cl2, C6H8Cl2, C6F5Cl3, C6H3F2Cl5, and the like, are also included in this bottom heavy stream that is sent to the vapor phase reactor, where such materials can cause the deactivation of catalyst.
As disclosed in U.S. Provisional Patent Application No. 61/604,629, filed Feb. 29, 2012, in an improved integrated process, a phase separator is used to receive the said bottom heavy stream so as to concentrate these non-recyclable high boilers. While the 1233xf contained in the HF phase of the separator is recycled back to the Step (1) reactor together with HF, substantial amounts of 1233xf and other recyclable byproducts such as 1232xf, 243 isomers, etc. are still present in the organic phase, together with non-recyclable high boilers. Due to the presence of high boilers, it is difficult to further isolate recyclable species using conventional distillation method. Hence, there is a need for means by which 1233xf and other recyclable byproducts can be efficiently recovered.